This invention relates to method and apparatus for monitoring brain activity and more particularly to method and apparatus that assesses brain activity by measuring cardiac pulse, preferably bilaterally, on a body.
It is desirable to be able to monitor brain activity such as for determining a sleep threshold or to determine “awareness” during surgery or to adjust dosage of anesthesia agents. Michael Airken, et al., in “Anesthesia Awareness and the Bispectral Index,” The New England Journal of Medicine, Mar. 13, 2008, vol. 358, No. 11, performed tests to determine the effectiveness of bilateral spectral analysis, BIS, for use during surgery to determine if a patient was experiencing “awareness.” Their analysis indicates that the technique does not provide a reliable method for this purpose, thereby leaving a vacuum for this type of measurement.
N. A. Laren, et al., in “Brain Function and Blood Flow,” Scientific American, October, 1978, made brain imaging measurements using positron emission tomography. These measurements provide observations of areas in the brain where mental activity was taking place during the execution of specific tasks. The method also provided estimates of blood flow to the brain. In general, a doubling in blood flow can be expected when a subject is carrying out active mental tasks. John Allen, et al., in “Similarity in Bilateral Photo-Plethysmographic Peripheral Pulse Wave Characteristics at Ears, Thumbs and Toes,” Physio. Meas. 21 (2000) 369-377, reported making bilateral pulse measurements at the earlobes. His work did not report changes in his measurements with mental activity.
It is an object of the present invention to measure cardiac pulses, preferably bilaterally, at the earlobes, forehead, or carotid artery at the neck to assess brain activity to determine, for example, a sleep threshold or to determine awareness during surgery.